1. Technical Field
This invention relates generally to battery charging systems, and more specifically to systems that recondition batteries by discharging prior to charging.
2. Background Art
When a nickel-based rechargeable battery is placed in a charger before it is completely xe2x80x9cdeadxe2x80x9d, it will lose some of its capacity due to the xe2x80x9cmemory effectxe2x80x9d. In other words, if a battery is consistently partially discharged before recharging, the battery will xe2x80x9cdiexe2x80x9d more and more quickly. In the worst case, a fully charged battery that originally lasted for four hours might die after only one hour.
This phenomenon is known as the memory effect, or voltage depression. It is particular to nickel chemistry batteries where the capacity, or in technical terms the xe2x80x9cenergy versus time curvexe2x80x9d, changes based upon discharge patterns. The good news is that the memory effect can be nearly eliminated by fully discharging the battery at a nominal current. This type of full discharge is called xe2x80x9creconditioningxe2x80x9d.
To keep a battery at original capacity, the battery needs to be reconditioned whenever the discharge time, i.e. the usable time of the battery, has become reduced. However, it is not always clear to the user when reconditioning is needed. Some chargers make the decision for the user. For example, U.S. Pat. No. 5,942,878, issued to Ito, entitled xe2x80x9cMethod and Device for Reducing Memory Effect of a Batteryxe2x80x9d, discloses one such charging system. The charger reconditions the battery every Nth charge depending upon usage.
The problem with these battery systems is that they sometime choose to recondition the battery when it is inconvenient for the user. For example, when the user is in a hurry and wants to charge the battery quickly for a special event, he will become frustrated when the charger starts a reconditioning cycle, thereby doubling the charge time. Likewise, if the user wants to recondition his battery right now, he may be frustrated when the charger does not think the time is appropriate.
Manufacturers have tried to overcome this problem by incorporating manual recondition switches in the chargers. For example, the 100-Watt 4 Station charger manufactured by ESI Technology includes a Mode Selector Switch that selects between charge and recondition modes.
The problem with mechanical switches is that they add cost to the end product. Additionally, they are mechanical parts that may fail after repeated use. There is thus a need for an improved method and apparatus for initiating reconditioning of batteries.